1. Field of the Invention
The present invention relates to a manufacturing method of a semiconductor multi-layer film and of a semiconductor laser.
2. Description of the Prior Art
Recently, a visible semiconductor laser of 600 nm band of AlGaInP system has been developed actively for a light source for an information processing apparatus such as a laser printer or an optical disk drive.
A prior art semiconductor laser of transverse mode control type is manufactured by using an epitaxial growth process including at least twice epitaxial growth steps with a metal-organic vapor phase epitaxial growth technique (MOVPE). FIG. 1 shows an example of a structure of a transverse-mode stabilized AlGaInP semiconductor laser. This semiconductor laser is manufactured as follows: In the first epitaxial growth step, a n-AlGaInP cladding layer 2, a GaInP active layer 3, a p-AlGaInP first cladding layer 4 and an n-AlInP current blocking layer 5 are layered on an n-GaAs substrate 1 successively. Next, a stripe-like groove is formed in the current blocking layer 5 by etching until the first cladding layer 4 is exposed. Then, in the second epitaxial growth step, a p-AlGaInP second cladding layer 6 and a p-GaAs contact layer 7 are layered successively over the groove. Next, electrodes 12 and 13 are formed at both sides.
In this manufacturing method, it is a problem that the repetition of the temperature increase and the regrowth on the AlGaInP layer causes the self-diffusion of doped impurities. For example, when selenium is doped in the n-AlInP current blocking layer 5 of the order of n=2.times.10.sup.18 cm.sup.-3, selenium atoms diffuse in the direction of the GaInP active layer 3, and this also enhances the diffusion of zinc of the dopant in the p-AlGaInP first cladding layer 4. Therefore, the carrier density profile in each layer changes in the regrowth and the position of the pn junction is not reproducible. Further, the diffusion of zinc into the GaInP active layer 3 causes the disordering of the crystal structure of GaInP and this makes the oscillation frequency unstable. A similar phenomenon may arise when the doping amount of the selenium is lower than that in the abovementioned case.
This phenomenon is a problem on the improvement of the characteristics of AlGaInP semiconductor laser and the increase in the yield thereof. This is also a problem in general on forming an n-type layer on a p-type layer in a semiconductor multi-layer film with the desired carrier profile reproducibly.